His example works OK, but the maths is not quite right. In fact, that is why
I realised something was fishy. What he calls 'difference frequencies' is
actually 'sum frequencies' (and vice-versa).
 
Not sure what it means for your UHJ converter. But it's worth
checking it. If you take the 1st out to be a cos, then the second is
-sine, not sine. So it's sine and cos, not cos and sine.
 
If you want to re-check my conclusion, it's simple. Put a sine through
hilbert, output the two sigs in stereo and compare their phases. You'll see
that the sine (imag) is the first output and the cos (real) is the second.

Victor

----- Original Message -----
From: matt ingalls <development@gvox.com>
Date: Sunday, October 28, 2007 10:56 pm
Subject: Re: [Cs-dev] Hilbert bug
To: Developer discussions <csound-devel@lists.sourceforge.net>

>

hmm..  as the math is beyond me, what does this bug mean for existing implementation. more specifically, the 2 times i have used it:


+ in sean costello's single sideband AM frequency shifter:
http://www.csounds.com/udo/displayOpcode.php?opcode_id=50


+ converting B-format to stereo-uhj:


http://www.csounds.com/udo/displayOpcode.php?opcode_id=47




(and just to restate my opinion on backwards compatibility: 
   go forward!  
   throw the old code in an opcode plugin for anyone who
   needs it and then never look back! )


-m

On Oct 25, 2007, at 7:10 AM, Victor Lazzarini wrote:

(no it's not Goedel going about stuff...)

>
Still waiting for someone to reply on this. I rechecked and
the outputs are definitely reversed. Now how do we deal with
it: change the code or change the manual?

>
The former will break backward compatibility, but just changing the
manual will make it not very intuitive (outs being
imag, real instead of real,imag).

>
Victor

>
At 16:57 19/10/2007, you wrote:
(no it's not to with his plans for mathematics...)

>
anyway, after almost going crazy checking and
rechecking my equations, I realised that the
Hilbert transform filter seems to have its
outputs the wrong way round. What is the
cosine output is the sine output and vice-versa.
(No wonder I could not get some ideas to work
properly.)

>
Can someone double-check this before we fix it?
(I used a sine input and checked the two signals
against each other. The 2nd output was in the
cosine phase against the 1st one in the sine
phase, but at this point I might be wrong).

>
This also explains why the example in the manual
has its up and down shifts the wrong way round too.

>
Victor

>
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>
Victor Lazzarini
Music Technology Laboratory
Music Department
National University of Ireland, Maynooth

>

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> matt ingalls
development@gvox.com





>

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